Unity 5 Parallax occlusion artifacts

when getting close to a surface that uses the new standard shader with a heightmap i get strange artifacts. looky here:
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its circle shaped, so it occours at a certain distance from the camera. the heightmap is a simple black and white image. the height multiplier is set to 0.0174. if i reduce it to its minimum 0.005 the artifact gets thinner, but is still visible. when cranking it up to max everything gets distorted. here i used a test texture:
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it seems to be a problem with the model importer. im letting it calculate the tangents but import the normals. when i also calculate the normals the image changes a bit but i still get the artifact. if i now decrease the smoothing angle to 0 the artifacts go away. but i want smooth shading on my models. or does parallax occlusion only work with flatshading?

It works best with correct normals. So in your instance, the floor is a flat surface, so it should be shaded as flat. Probably you can mark only the floor sharp in your modeler, so the rest won’t be affected.